In this specification, where a document, act or item of knowledge is referred to or discussed, this reference or discussion is not an admission that the document, act or item of knowledge or any combination thereof was at the priority date part of common general knowledge, or known to be relevant to an attempt to solve any problem with which this specification is concerned.
Continuous toothed belts capable of power transmission are often referred to as timing belts or cam belts, acknowledging their common application as a part of an internal combustion engine to control the timing of the engine's valves. Such belts are usually flat and incorporate integral teeth, although other profiles, such as V-belts, are also known, and for certain applications the teeth may be separately formed and connected to a planar flexible belt web.
The teeth of the belt fit into matched toothed pulleys, or sprockets. When correctly tensioned, there is no slippage between belt and pulley/sprocket, affording accurate synchronisation between the rotations of drive and driven pulleys/sprockets.
Non-automotive applications include use in any mechanism where it is necessary to interchange rotary motion and linear motion, where either high loads are encountered or maintaining a specific drive ratio (eg. for indexing purposes) is important, and where chain drives might alternatively be used. A common non-automotive application is in linear positioning systems. While chains and gears may be more durable, flexible belts are generally quieter in their operation, are considerably lighter (and hence mechanically more efficient), and can be less expensive.
Typically, a timing belt is made of rubber incorporating high-tensile fibers, such as steel, fibreglass or aramid (eg. Twaron™/Kevlar™) running the length of the belt. For high temperature applications, belts may be made of temperature-resistant materials such as highly-saturated nitrile (HSN) materials.
Conventionally, belts have trapezoid-shaped teeth, but newer manufacturing techniques allow for production of curved teeth that can have the advantage of being quieter in operation and lasting longer.
For some applications, such as use as an automotive engine timing belt, the belt must be continuous and unbroken, and the ends of the belt length are generally welded together by the manufacturer. For applications of linear positioning, such as driving automatic barriers, gates or doors, it is common to supply lengths of belt stock for cutting to length and installation as required. In such applications, a connector means is required to hold the ends of the belt in a fixed relative position. Commonly, the ends of the belt may be attached to the connector means by fasteners (eg. by screws) or by crimping or clamping of shaped jaws. However, such devices can damage or weaken the belt, and make later adjustment or refitting of the same belt (eg. during maintenance) difficult or impossible.
Both chains and flexible drive belts are commonly used in drive assemblies for doors, gates or barriers, such as garage door drives. In such drive assemblies for overhead doors or sectional doors, the chain or belt is generally arranged in a closed loop between an idler sprocket and a drive sprocket, and a trolley or carriage connected thereto is mounted to slide along or within an overhead longitudinal rail, the trolley or carriage attached by means of a suitable linkage to the door. An electronically-controlled motor unit selectively drives the chain or belt, so moving the door between open and closed positions.